The discovery of a large number of maps of the visual field in the cerebral cortex has led to the hypothesis that each visual area performs its own set of functions in visual perception. At least nine cortical visual areas are present in the owl monkey, the Primate which has been mapped most completely. We seek to determine how visual information is processed in the owl monkey's visual areas by analyzing the neurophysiological response properties of single neurons. In earlier work we have found that a field of random dots resembling a moving surface is ia very strong stimulus for most neurons in the middle temporal visual area (MT). We propose to investigate the responses of MT neurons to a wide variety of computer-controlled video displays that simulate moving surfaces. These displays include patterns that stimulate Gibsonian visual flow, motion parallax and texture gradient cues for depth perception, and form embedded in texture. We propose to investigate the mechanisms of direction-specific adaptaion, the basis of strong visual illusions such as the motion after-effect, in the directionally selective cell populations in the primary visual area (V-I) and MT. We have found that most neurons in the dorsolateral visual area (DL) are sharply tuned to stimulus dimensions (length and width) independent of position and contrast in their excitatory receptive fields, and we seek to determine whether there exists a columnar system for dimensional preferences in DL analogous to the columnar system for orientation selectivity in V-I. We also seek to determine whether DL neurons are tuned by binocular disparity since stereoscopic depth tuning coupled with dimensional preference could contribute to the mechanism of size constancy, the judgment of the actual size of objects at different distances. The discovery of the functions of the cortical visual areas is likely to have far-reaching implications for the understanding of the mechanisms of visual perception and for the diagnosis of neur-ophthalmological disorders.